Work in co-operative (5)
I believe the answer is:
opera
'work' is the definition.
(musical work)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for opera that I've seen before include "Lohengrin, say" , "Macbeth for one" , "art form" , "musical presentation" , "Billy Budd, for instance" .)